Recovery of powder in an electrostatic powder spraying operation

ABSTRACT

A filter chamber of a powder recovery apparatus has an inlet through which a powder-carrying air stream is admitted, and an outlet. Filter elements are interposed between the inlet and the outlet to intercept and retain the powder particles, and a pneumatically operated vibrating arrangement can vibrate the filter elements within the chamber so as to separate the retained powder particles from the filter elements. A collecting bin is provided below the chamber for collecting the separated powder particles. Details of the construction of the vibrating arrangement and the filter elements, as well as of the collecting bin, are also disclosed together with details of a safety arrangement which operates in the event of blocking, deflagration or should actual combustion occur at the spraying station of the installation with which the recovery apparatus cooperates.

[ Aug. 12, 1975 RECOVERY OF POWDER IN AN ELECTROSTATIC POWDER SPRAYING OPERATION Herbert Rapp, Karlstr. 52, 7410 Reutlingen, Germany 221 Filed: Apr. 18,1973

211 Appl.No.: 352,298

[76] Inventor:

[30] Foreign Application Priority Data Apr. 20. 1972 Germany 2219314 Mar, 14, 1973 Germany 2312560 [52] U.S. CI. 55/283; 55/272; 55/300;

[56] References Cited UNITED STATES PATENTS 1,751,138 3/1930 Eihen 55/300 3,212,643 l0/l965 Schmidt. Jr. et a1 3,489,464 l/l970 Delfs 302/59 3,636.680 l/1972 Seidel 55/291 3,699,747 10/1972 Kroll 55/302 FOREIGN PATENTS OR APPLICATIONS 738,305 10/1932 France ..55/300 940,896 11/1963 United Kingdom ..55/305 Primary ErarninerBernard Nozick Attorney, Agent, or Firm-Michael S. Striker 5 7 1 ABSTRACT A filter chamber of a powder recovery apparatus has an inlet through which a powder-carrying air stream is admitted, and an outlet. Filter elements are interposed between the inlet and the outlet to intercept and retain the powder particles, and a pneumatically operated vibrating arrangement can vibrate the filter ele ments within the chamber so as to separate the retained powder particles from the filter elements. A collecting bin is provided below the chamber for collecting the separated powder particles. Details of the construction of the vibrating arrangement and the filter elements, as well as of the collecting bin, are also disclosed together with details of a safety arrangement which operates in the event of blocking, deflagration or should actual combustion occur at the spraying station of the installation with which the recovery apparatus cooperates.

20 Claims, 3 Drawing Figures Suction SOUICS IPATENTEU mm 21% SHEET 3 4 a 5 w up w PATENTEU AUG 1 2197s SHEET Fig.2

pneumatic fluid PATENTED AUG] 2 I975 SHEET RECOVERY OF POWDER IN AN ELECTROSTATIC POWDER SPRAYING OPERATION BACKGROUND OF THE INVENTION The present invention relates to a powder recovery apparatus, and more particularly to an apparatus for recovering excess powder in an electrostatic powder spraying installation.

The technique of electrostatic powder spraying is well enough developed not to require a very specific description herein. It is mentioned in the Dictionary of Mining, Minerals and Related Terms issued by the U.S. Department of the Interior, and it is discussed in detail in Dodds Dictionary of Ceramics issued by the Philosophical Library, New York. In summary it may be said, however, that electrostatic powder spraying, hereafter called EPS for short both in the specification and in the appended claims, involves the deposition of powder particles on an object which is to be coated with them. The most frequently used material is a synthetic plastic powder, usually on the basis of epoxy resins, which is electrostatically charged in a spray gun. The workpiece, that is the article to be coated, is grounded and when the positively charged powder particles are propelled at it, they will electrostatically adhere to the workpiece. When the workpiece is thus provided with a coating of the powder particles it is placed into a kiln and heated to a temperature at which the particles of the coating will melt and form smooth continuous layers on the workpieces. These layers usually have a thickness of between 70 and l microns and the technique is most commonly employed for depositing coloring matter on a workpiece.

It is hardly necessary to point out that as in almost all spraying operations, a significant proportion of the powder expelled by the spray gun in an EPS installation will not become deposited on the workpiece. Such excess powder will initially float freely in the spray booth and, if permitted to do so, will subsequently settle on the walls and floor of the booth and become lost for further use. Evidently, such losses of valuable material are economically unacceptable so that an important as pect of EPS installations is the recovery of the excess powder. This is accomplished by withdrawing a stream of air carrying the excess powder from the spray booth and passing it through a filtering arrangement which retains the powder particles. The filter elements of the filtering arrangement are intermittently vibrated so that the retained powder loosens and falls off into an appropriate receptacle located beneath the filter element. From this receptacle the collected powder is trans ported to a screening device wherein it is screened to separate the acceptable and recoverable fraction from the fraction which must be discarded. The recovered fraction can then be proportionately admixed with new powder to be supplied to the spray gun.

Depending upon the required capacity and the number of colors (different-colored powders) it is frequently desirable to combine two or more powder recovery apparatuses in an EPS installation. It is for instance known from the prior art to provide two such apparatuses which are mounted on a common frame but have different filter chambers. A common powder recovery bin and/or a common recovered-powder conveyor (such as a conveyor screw) is provided for these two (or for more) recovery apparatuses.

However, the prior art has certain disadvantages. In particular, the powder recovery apparatuses known heretofore are relatively large, especially with respect to their height. This is frequently not desirable because space is often at a premium in such installations. Another drawback is the fact that it is not possible to combine such apparatuses in building-block fashion, that is to use each such apparatus as a module, so that any desired number of apparatuses can be located closely adjacent to one another with a minimum loss of space, preferably in such a manner that the walls of adjacent apparatuses contact one another.

A further difficulty of the prior-art apparatuses of the type in question is that they are not well protected against explosion or fire, two hazards which constitute a definite problem in EPS installations.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to overcome the aforementioned disadvantages of the prior art.

More particularly it is an object of the present invention to provide an improved powder recovery apparatus, especially suitable for use in EPS installations, which avoids these disadvantages.

Another object of the invention is to provide such a powder recovery apparatus which can be constructed so compactly and in such a manner as to require a minimum of space.

An additional object of the invention is to provide such an apparatus whose configuration and dimensions are such that two or more such apparatuses can be readily combined in modular form, that is that an assembly of any desired number of such apparatuses can be produced by the building-block system.

A further object of the invention is to provide such an apparatus which is well protected against hazards such as explosion and fire.

In keeping with the above objects, and with others which will become apparent hereafter, one feature of the invention resides, briefly stated, in a powder recovery apparatus which is especially-although not exclusivelysuitable for use in electrostatic powder spraying installations and which comprises a filter chamber having an inlet and an outlet. Filter means is located intermediate the inlet and the outlet for intercepting powder particles in a gas stream admitted through the inlet. The filter means comprises substantially upright suspended filter elements having lower end portions which are engaged by a vibratory frame. Suction means communicates with the outlet and collecting means is located beneath the filter means for collecting powder particles and intercepted by the same. Vibrating means is connected with the frame for vibrating the same so as to effect the release of intercepted powder particles from the filter means for collection in the collecting means. The vibrating means comprises a pneumatic cylinder and piston unit including a piston rod and a weight carried by the latter, and an air-impulse valve cooperating with this unit for imparting oscillatory movement to the weight.

An apparatus so constructed can have particularly small and compact configuration, and can be readily so configurated that it can be installed with one or more similar apparatuses to form an assembly or system in the manner in which building blocks are assembled by placing them side-by-side.

The novel features which are considered characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a perspective view of an apparatus according to the present invention, with one wall of the housing of the apparatus omitted for the sake of clarity;

FIG. 2 is a somewhat diagrammatic section taken on line II-II of FIG. 1; and

FIG. 3 is a diagrammatic side view illustrating a further embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing firstly the embodiment illustrated in FIGS. 1 and 2 of the drawing, it will be seen that the powder recovery apparatus in itself has three major sections, namely a filter chamber 1 having an inlet 2 for powder-carrying air, an upper housing section which is connected by means of non-illustrated clamps or the like with the walls bounding the chamber 1, and a lower collecting receptacle or bin 7 which is also releasably connected with the walls of the filter chamber 1 by means of non-illustrated clamping devices or the like.

Located in the interior of the chamber 1 is a plurality of approximately vertical, here plate-shaped filter elements 3 whose upper ends are suspended from an upper mounting element 17 and whose lower free ends are engaged by a vibratory frame 18 which can be vibrated by vibrating means 4.

At the upper end the chamber 1 is open to and communicates with the interior of the housing section 5 which is subdivided by a partition wall into a venting chamber 6 and a suction channel 9. The chamber 6 communicates with the channel 9 via an opening which can be opened and closed by an appropriate device, here illustrated as a plate valve 11 which in the embodiment of FIGS. 1 and 2 is actuated by a hydraulic cylinder and piston unit 12. The channel 9 itself communicates with the diagrammatically illustrated suction source, for instance the suction side of an exhaustor of known construction. In addition, the channel 9 has an air inlet port which can be opened and closed by a further plate valve 13 (or other analogous device) which in turn is operated by an associated pneumatic cylinder and piston unit 14.

In operation of this apparatus a non-illustrated timer is used to pre-set the desired time period during which the suction source draws a stream of air through the chamber 1 and the inlet 2 which is connected with a source of powder to be recovered, such as the spraying station of an electrostatic powder spraying installation. The air is drawn through the filter elements 3 on which latter the powder particles carried by the air stream are intercepted and retained. During this time the valve 1 l is in open position and the valve 13 in closed position.

When the preselected time period has ended, a nonillustrated program control (well known and for instance of the type using rotary cams) is activated which sequentially opens the valve 13, closes the valve 11, starts operation of the vibrating means 4 and-after a programmed time delay-again terminates the operation of the vibrating means 4, opens the valve 11, and finally closes the valve I3. It is evident that with this operation the suction source need not be disconnected from the channel 9 and can continue to exert suction, except that now (that is while the accumulated powder particles are separated from the filter elements 3 and permitted to accumulate in the bin 7) air is drawn not through the filter chamber 1 but from the exterior thereof through the opening controlled by the valve 13. This eliminates the necessity for shutting down the suction source or disconnecting it from the channel 9, and at the same time permits initiating of the vibration of the filter elements 3 for the purpose of separating the accumulated and retained powder particles therefrom, as soon as the valve 11 has closed.

It will be appreciated that this operation is highly beneficial. All known filtering systems utilizing cloth filters for maintaining filtered powder thereon require that the filter chamber be disconnected from any source of suction or pressure at the time the accumulated powder is removed from the filter element. Unlike the present invention, however, the known con structions either must shut down the suction source or must disconnect the same from the filter unit and during the period during which the accumulated particles are removed from the filter elements of the filter unit the suction source is connected with a second filter unit. The latter approach is used particularly in installations in which automatic removal of the accumulated powder from the filter elements is carried out.

By contrast to this, the present invention in effect diverts the stream of air flowing to the suction source so that the suction source need be neither disconnected nor shut down. Thus, immediately after the valve 11 is in closed position the removal of accumulated powder from the filter elements 3 by operation of the vibrating means 4 can be initiated, and conversely the filtering operation can be immediately restarted after the vibrating means 4 is shut down, simply by opening the valves 11 and closing the valves 13. The valves could, incidentally, be actuated by means other than the illustrated pneumatic cylinder and piston units, but in any case the present invention permits the removal of accumulated powder from the filter elements 3 to be carried out very rapidly so that the time period during which no powder-carrying air is being drawn through the filter elements can be reduced to mere seconds. This makes it possible to utilize the apparatus according to the present invention in many instances where heretofore much more elaborate and expensive automatic filtering and recovering devices were required.

As FIG. I shows particularly clearly, the top wall of the housing section 5 is provided with an opening which is normally closed by a hinged flap 15. The latter is urged to closing position by a restoring spring 16 which in the illustrated embodiment is connected at its opposite ends to the flap I5 and a side wall of the housing section 5, respectively. The purpose of this arrangement is to provide a pressure-relief system so that, if pressure in the chamber 6 rises above a certain level which is preset by the characteristics of the spring 16, the flap 15 will be upwardly displaced against the force of the spring 16 to permit venting of the chamber 6. When the pressure in the chamber thereupon drops, the spring 16 restores the flap 15 to the closure position shown in FIG. I.

38. In this manner I assure a uniform fluidization of the powder in the respective sections 35 and 36. Located above the section 35 is an injector-type conveyor 8 which receives the fluidized powder and conveys it to an external location (such as a storage hopper) via the outlet conduit 39. The uniform fluidization of the powder obtained by the separate provisions of the sections 35 and 36 and their separate air supply assures that the powder will freely flow to the conveyor 8 to be entrained by the same. The conveyor 8 operates on the well known injector principle, which is known for instance from steam jet pumps or water pumps and requires no detailed discussion. The powder leaving through the outlet conduit 39 can be supplied (e.g., via a small cyclone) to a screening device which may be located above the powder hopper of the electrostatic powder spraying installation or above a separate container.

The utilization of two (or more) fluidization sections such as those designated with reference numerals 35 and 36 has substantial advantages, as does their separate supply with fluidization air. Particularly in collecting bins having rectangular fluidization sections of horizontal orientation problems were heretofore encountered with the movement of the powder being fluidized. A pneumatic removal of the powder (via a device such as the injector 8) causes withdrawal of the powder in the region of the removal device and a consequent change in the flow resistance encountered in this region by the fluidizing air. As a result, the air will flow more rapidly in the region where powder is being withdrawn, whereas the regions located farther from the removal device are not so affected. The powder is therefore non-uniformly fluidized and will not properly flow in the direction towards the removal device. For this reason the collecting receptacles in known powder recov' ery apparatuses all use strongly sloping bottom walls which are usually inclined to the horizontal at an angel of 45, or certainly not much less. Moreover, these known apparatuses use powder collecting receptacles which converge in downward direction (towards their bottom wall) as much as possible to overcome the aforementioned problem. However, given the fact that these receptacles must have a certain volumetric capacity it is clear that such convergence to make the width of the bottom wall as small as possible requires that the receptacles be relatively high. The invention overcomes this problem and prevents non-uniform fluidization of the powder in the receptacle 7'. Thus, the powder will much more readily flow towards the device 8 which in turn makes it possible to provide a bottom wall 34 of relatively large area which can be completely or almost completely horizontal, thus permitting a much lesser height for the collecting receptacle 7 and reducing the overall height of the apparatus still further.

FIG. I shows particularly clearly that the overall dimensions, particularly the height of the apparatus according to the present invention, are significantly smaller than what is known from the prior art. This makes it possible for two or more such apparatuses, each of which is provided with a frame 40 on which it is mounted, to be placed closely adjacent to one another and to assemble as many of the apparatuses, and in as varied a pattern as desirable, in the manner of building blocks. The frames 40 can then be connected with one another. Reference numeral 41 diagrammatically illustrates the possibility of providing a nonillustrated control box which is connected with the apparatus.

The EPS technique was originally thought to be without any particular problems, especially problems relating to the possibility of danger. However, when automatically operating EPS installations were devised it was found that a danger of possible powder explosion did exist. In these automatically operating installations the workpieces are introduced by a conveyor into a spray booth in which the spray guns directs positively charged powder particles against them. To avoid sparking the workpieces are grounded via the conveyor. It is, however, possible that the workpieces are not properly held on the conveyor and therefore not properly grounded, or that the workpieces might for other reasons not be properly grounded, or again that the grounding of the conveyor itself might become defective. In such an event sparking between the incoming workpiece and the spray gun which is connected to high tension can occur, and if a powder-dust concentration of 5055 g/m is present in the air in the region where spraying takes place, this can result in a static deflagration of the powder. In turn, a tire or an explosion can result.

Evidently, this possibility must be counteracted and therefore it was decided that in the event of a fire the supply of further powder to the spray gun, the connection of the spray gun to high tension, and the withdrawal of powder from the spray booth to the powder recovery apparatus would have to be terminated immediately. It is therefore known for this purpose to provide in the spray booth a plug of material which melts at requisite temperature, for instance Babbit metal, to sense the occurrence of elevated temperatures associated with the development of fire and to trigger a signal which shuts down the powder supply and the high tension supply, and at the same time closes a valve interposed in the conduit leading to the powder recovery apparatus. Unfortunately it has been found that this arrangement is not fully satisfactory. The major reason for this is that the aforementioned sensing arrangement will operate only when the temperature has exceeded a certain level, that is only when a fire is already in progress. It will not operate if sparking occurs so that the connection between the spray booth and the powder recovery apparatus is terminated only when a tire already has started in the spray booth. Moreover, since at this time the suction source associated with the powder recovery apparatus still continues to draw powdercarrying air out of the spray booth the flames will be rapidly drawn into the conduit connecting the spray booth with the powderrecovery apparatus and will frequently be able to reach the filter elements in the latter before the safety valve in the conduit can close the latter off. It has been attempted to overcome this problem by having the sensor-initiated signal shut off the suction source, but this is not effective because the suction source in such installations is a blower which, even though it is shut off, will only gradually cease to draw a stream of powder-carrying air out of the spray booth.

The embodiment illustrated in FIG. 3 avoids these aforementioned problems and very substantially increases the safety of operations in an EPS installation.

Referring to FIG. 3 it will be seen that reference numeral 50 designates a spray booth of an EPS installation. A conduit 51 connects the spray booth 50 with a As FIGS. 1 and 2 show, the cross-section of the filter chamber 1 is right-angular, and in the illustrated embodiment it is quadratic. The upper end portions of the filter elements 3 are mounted in the upper mounting element 17, as previously pointed out. FIG. 2 shows that this is a member provided with a plurality of slots through which the upper end portions of the elements 3 extend, suspending devices being provided (see FIGS. 1 and 2) which suspend the elements 3 from the element 17 so that they have a certain freedom of movement in direction transversely to the elongation of the slots in the element 17. Evidently, two or more of the elements 17 could also be provided. The lower ends of the elements 3, on the other hand, are engaged in a vibratory frame 18 to which the vibrating means 4 is connected, so that the latter is located within the chamher 1 and the receptacle 7. This is a substantial advantage over the prior art. In the first place, the prior art locates the vibrating arrangement exteriorly of the housing so that it interferes with any attempt at placing two such apparatuses close together in side-by-side relationship in a building-block manner. Moreover, in the prior art the vibrations are transmitted not only to the filter elements but to the housing itself, and from there to the housing of the adjacent apparatus, if the latter is to be located relatively close. In the adjacent apparatus, however, this can lead tocompacting of the powder on the filter elements while the latter are subjected to suction. The present invention avoids this in that the vibrating means 4 is located within the filter chamber 1 and/or the collecting receptacle 7, so that no external interference with other apparatuses can occur. The transmission of vibrations to the housing of the apparatus is reduced to a minimum because of the fact that the filter elements 3 are freely suspended in the mounting elements 17, and that the frame 18 (as shown in FIG. 2) is so mounted in the chamber 1 by means of elastomeric straps, springs or other suitable devices, that a transmission of vibratory stresses to the housing is minimized. In addition, the construction according to the present invention has the further advantage that the prior-art problem of dust-tightly connecting the exterior vibrating device with the interior filter-vibrating frame does not exist and cannot occur. The entire pneumatically operated vibrating means 4 in the apparatus according to the present invention is dust-tightly located in the interior of the apparatus so that the problem of preventing the escape of dust or powder cannot even occur.

As shown in FIG. 2 the filter elements 3 are here configurated in form of filter plates and each has a filter frame 20 of U-shaped cross-section. Spaced about the opposite outer sides of the frame 20 is a filter cloth l9, and located within the respective frame 20 is an airpermeable support 21, advantageously in form of wire mesh or cloth. The support 21 of course serves to support the filter cloth l9 and I have found it advantageous if it is in form of two transversely spaced at least substantially parallel sections which are maintained spaced from one another by the illustrated spacers 22. A certain amount of play (indicated at 23 in FIG. 2) is permitted between the respective frame 20 and the associated support 2! so that the latter can flex during operation of the vibrating means 4, as indicated by the broken lines 24. This of course causes similar flexing of the filter cloth l9 and greatly facilitates the rapid removal of accumulated powder particles from the filter cloth.

Evidently, this measure permits a reduction in the time required for separating the accumulated layer of powder particles from the filter elements 3 and thus reduces the time period during which the apparatus does not receive powder-carrying air for filtration, that is the period during which powder is removed from the filter cloth of the filter elements 3. Also, as a result of this measure and the savings in filter-cleaning time obtained thereby, the filters can be cleaned more often than heretofore without thereby cutting down on the active (filtering) time of the apparatus. This, in turn, makes it possible to make the filter elements 3 of smaller size than would otherwise be the case, so that the dimensions of the overall apparatus, especially its height, can be lesser than in the prior art.

The vibrating means 4 of FIG. 1 is shown in more detail in FIG. 2. It will be seen that it comprises a housing 4a which is mounted on the frame 18 itself so as to have no direct connection with the housing of the apparatus. It utilizes a pneumatic cylinder and piston unit 25 which is mounted in the housing 4a and which is connected via the housing 4a with the frame 18 and whose use has the particular advantage that it eliminates any,

need for providing protective devices intended to prevent dust explosions. This problem cannot occur when a pneumatic cylinder and piston unit is used. The piston of the unit 25 is diagrammatically illustrated and will be seen to carry on its free end portion a weight 28. It re ceives compressed gas from the diagrammatically illustrated external source via a flexible conduit 29 (e.g., a metallic or rubber hose). Via an air impulse valve 27 the incoming compressed air imparts to the piston of the unit 25 an oscillatory movement in the direction of the double-headed arrow 26, and the presence of the weight 28 imparts enough magnitude to this movement to vibrate the filter elements 3 with sufficient force to dislodge powder particles retained on their respective filter cloths 19. The compressed air is vented into the housing 4a and from there to the exterior of the apparatus via a further flexible conduit 30, which may again may be a rubber or metallic hose. This arrangement is substantially superior to the known construction utilizing an electromotor mounted at the exterior of the apparatus housing, so that the time required for removing retained powder particles from the filter cloths 19 by the vibration step is reduced. This, in turn, also means that the vibration step can be carried out more often than was heretofore the case and that, in consequence, the dimensions of the filter elements 3 can be kept smaller than previously, leading to a more compact construction of the apparatus, especially to a lesser height.

The cross-section of the receptacle 7 corresponds to that of the filter chamber 1, i.e., in the illustrated embodiment it is quadratic. As FIG. 1 shows, the receptacle 7 has two substantially vertical end walls 31 and 32. In addition, it has outwardly inclined side walls 33 (one of which is omitted in FIG. 1 to show the interior of the receptacle 7) and an at least substantially horizontal bottom wall 34. The bottom wall 34 issubdivided into two separate fluidizing sections 35 and 36 on which the accumulated powder particles can be fluidized (in the manner of a fluidized bed) by passing a stream of air upwardly through them. For this purpose each of the sections 35 and 36 (having a plurality of capillary apertures of approximately lp. width) is separately supplied with compressed air via respective inlet valves 37 and powder recovery apparatus 52 of the type described with respect to FIGS. 1 and 2. Workpieces 53 are automatically introduced into the spray booth 50 by means of the diagrammatically illustrated conveyor 54. The conveyor 54 is grounded in known manner and the workpieces 53 are so connected with it as to be grounded in turn. A spray gun S of known construction is provided which is connected with a high tension unit 55a so that powder particles which are sprayed from the spray gun 55 against the workpieces 53 will be positively charged.

Excess powder, that is those powder particles which do not adhere to the workpiece 53, are drawn out of the spray booth 50 via the conduit 51 into the powder recovery apparatus 52. Like reference numerals applied to the apparatus 52 in FIG. 3 refer to the same components shown in FIGS. 1 and 2. In FIG. 3, however, the receptacle 7 is provided with an outlet 56 for the removal of the collected recovered powder particles. The source of suction is here identified with reference numeral 57 and shown as an exhaustor.

The valves 11 and 13 are employed in the same manner described with respect to FIGS. 1 and 2, and an electrical timer 58 is provided which is connected in circuit with a programmer 59 of commercial size (Firma Max Stegmann, Donaueschingen, Germany) and via the same with valves 11 and 13 to permit preselection of the time during which powder-carrying air is to be drawn through the filter elements. After expiration of this time the programmer 59 which may utilize a camshaft gear cams of which control limit switches for its control functions, initiates via the conductors 60 and 61 a programming sequence which involves the opening of the valve 13, closing of the valve 11, starting and subsequent stopping of the filter element vibration, opening of the valve 11 and closing of the valve 13. During this time the exhaustor 57 continues to operate.

A photoelectric cell or eye 62 is mounted in the spray booth 50 and is of such construction that it will react by producing a signal as soon as sparking occurs in the region between the spray gun 55 and the workpiece 53. The cell 62 is connected via a conductor 63 to a control unit 64 of commercial size including a multiple switch which, when it receives a signal from the cell 62, triggers at one and the same time the following functions: it shuts off the high tension unit 55a via a conductor 65, it shuts off the powder supply to the spray gun 55 via a conductor 66, it shuts off the exhaustor 57 via a conductor 57, it closes the valve 69 in the conduit 51 via a conductor 68, and via a conductor 70 and a relay 71 it closes the valve 11 and opens the valve 13. All of this is carried out in fractions of a second. Thus, as soon as sparking occurs the arrangement according to the invention will not only close off the connection between the booth 50 and the apparatus 52, but will also divert any residual air stream being drawn into the exhaustor 57 (until such time as the latter has come to a standstill) to the ambient atmosphere so that air is drawn through the opening controlled by the valve 13 and no longer through the conduit 51.

The cell 62 serves in this embodiment to detect sparking. To provide further safety against dangers sub sequent to and resulting from such sparking there is provided a fusible element 72, for instance of Babbit metal or the like, which is also located in the spray booth 50 and which will melt in the event flames actually develop in the booth. The element 72 is connected with a multiple switch 72a and thereupon via a conductor 73 with the control unit 64, and via a conductor 74 with a fire extinguisher 75 (preferably on CO basis) that is also arranged in the booth 50. Thus, when a signal is derived from the element 72, the control unit carries out the same control functions as outlined above but in addition the fire extinguisher 75 is triggered and will begin to operate.

With the arrangement illustrated in FIG. 3 the flow of an air stream from the booth 50 into the apparatus 52 is abruptly terminated as soon as sparking occurs, and there is no need to wait for the exhaustor 57 to come to a standstill before the airstream will completely cease. This significantly reduces the danger that in the event flames should develop in the booth 50 such flames might be drawn into the apparatus 52 through the conduit 51 before or during the closing of the valve 69. In fact, the safety factor is greatly improved, even if the photocell 62 were to be replaced by a sensor that responds only to an increase in temperature or pressure, that is that would respond when actual combustion is already taking place in the booth 50. Of course, the use of the cell 62 to detect sparking provides optimum results because it initiates the safety measures at the earliest possible time.

Naturally, the photocell 62 could be replaced by a thermal sensor responsive to increased temperature in the spray booth 50 and/or by a different type of sensor which might for instance react to a pressure increase or to deflagration in the booth 50. In so far as the photocell 62 is concerned any appropriate photocell well known to the art can be utilized, for instance a photodiode, a phototransistor, a photoresistor, a photocell in general, or a photomultiplier tube, but currently preferred for the purpose of the invention is a so-called photo-eye of commercial size of the SAMES S.A., Grenoble (France), functioning on the basis of a photoresistor.

It will be seen that with the invention as disclosed herein significant advantages are obtained over the prior art. Not onlyis it possible to provide a powder recovery installation of desired size, merely by combining any desired number of the disclosed powder recovery apparatuses, but also any increase or decrease in the size of such an installation can be readily accomplished merely by adding additional building blocks in form of further powder recovery apparatuses or removing them. The apparatuses themselves can physically be constructed in substantially box-shaped configuration, having straight or substantially straight outer walls so that adjacent apparatuses can be placed closely together or even into contact with one another.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in a powder recovery apparatus, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that from the standpoint of prior art fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

1. A powder recovery apparatus for use in EPS installations, comprising a filter chamber having an inlet portion and an outlet portion; filter means in said filter chamber intermediate said inlet and outlet portions thereof for intercepting powder particles from a gas stream admitted through said inlet portion; collecting means beneath said filter means; vibrating means operatively connected with said filter means for vibrating said filter means so as to release intercepted powder particles for collection of the same by said collecting means; a source of suction; a suction channel interposed between and communicating with said source and said outlet portion, said suction channel having an intake port for ambient air at atmospheric pressure from the exterior of the apparatus; first valve means between said outlet portion and said suction channel to open and close said outlet portion to suction; second valve means in said intake port; and control means connected to said valve means for displacing said first and second valve means between closed and open positions thereof so that said source draws said gas stream into and through said filter chamber and said suction channel when said first valve means is in said open position thereof with attendant interception of the powder particles from said gas stream by said filter means, whereas ambient air from the exterior of the apparatus is drawn by the source into said suction channel through said intake port when said second valve means is in said open position thereof and while said first valve means is in said closed position thereof with attendant interruption of the passage of gas stream through said filter chamber.

2. An apparatus as defined in claim 1; and further comprising suspending means for freely swingably suspending said filter elements in said filter chamber.

3. An apparatus as defined in claim 1, wherein said control means includes means for pneumatically actuating said valve means.

4. An apparatus as defined in claim 1, wherein said control means is operative for closing said first valve means and opening said second valve means during the operation of said vibrating means whereby the passage of said gas stream through said filter chamber is interrupted and the released powder particles are collected by said collecting means.

5. An apparatus as defined in claim 1, wherein said filter means comprises substantially upright suspended filter elements having lower end portions; and a vibratory frame engaging said lower end portions; and wherein said vibrating means is connected with said frame for vibrating the same so as to effect release of intercepted powder particles from said filter means for collection in said collecting means, said vibrating means comprising a pneumatic cylinder and piston unit including a piston rod and a weight carried by the latter, and an air-impulse valve cooperating with said unit for imparting oscillatory movement to said weight.

6. An apparatus as defined in claim 5, wherein said frame is freely swingable, and wherein said vibrating means is located in said chamber and carried by said frame.

7. An apparatus as defined in claim 6; and further comprising a flexible conduit connecting said vibrating means with a source of hydraulic fluid.

8. An apparatus as defined in claim 1, wherein said filter means comprises a mounting member, a vibratory frame downwardly spaced from said mounting member, and a plurality of substantially plate-shaped filter elements suspended from said mounting member and including gas-permeable supports having lower end portions engageable by said frame and capable of flexing in the direction in which said frame vibrates, and filter cloths externally surrounding the respective supports so as to flex with the same, whereby powder particles retained on said cloths are released from the same; and wherein said vibrating means is connected with said frame for vibrating the same so as to effect release of said powder particles for collection thereof in said collecting bin.

9. An apparatus as defined in claim 8, wherein said supports are of wire cloth.

10. An apparatus as defined in claim 8, wherein said supports each comprise two substantially parallel spaced support sections, and spacer means between said sections so as to maintain them spaccc apart.

11. An apparatus as defined in claim 8, wherein said end portions of said supports have limited freedom of play relative to said frame.

12. An apparatus as defined in claim 1, and wherein said collecting means comprises a receptacle having a bottom wall subdivided into a plurality of fluidizing sections, and supply means for supplying each of said sections independently with a fluidizing gas so as to fluidize the collected powder particles in said receptacle.

13. An apparatus as defined in claim 12, wherein said bottom wall is subdivided into two of said fluidizing sections.

14. An apparatus as defined in claim 12, wherein said bottom wall is substantially horizontal, and wherein said receptacle is of right-angular cross-section and comprises a pair of substantially vertical end walls and a pair of upwardly inclined side walls; and further comprising injector-type conveying means in said receptacle above one of said sections for conveying fluidized powder particles out of said receptacle.

15. An apparatus as defined in claim 14, wherein said receptacle is of substantially quadratic cross-section.

16. An apparatus as defined in claim 1; further comprising conduit means for connecting said inlet portion with a spraying station for spraying powder into a workpiece; and wherein said control means includes sensing means for sensing the occurrence of a condition incident to combustion of powder at said station, said control means being operative for closing said first valve means and opening said second valve means in response to a sensing signal received from said sensing means.

17. An apparatus as defined in claim 16, wherein said sensing means comprises a photoelectric cell.

18. An apparatus as defined in claim 16, wherein said sensing means comprises a photoelectric cell operative for detecting the occurrence of sparking at said station.

19. An apparatus as defined in claim 16, wherein said sensing means comprises a sensor capable of sensing the occurrence of at least one of the combustion incident conditions of sparking, deflagration and combus tion.

20. An apparatus as defined in claim 16; further comprising an valve interposed in said conduit means and operative for blocking the same in response to operation of said control means. 

1. A POWDER RECOVERY APPARATUS FOR USE IN EPS INSTALLATIONS, COMPRISING A FILTER CHAMBER HAVING AN INLET PORTION AND AN OUTLET PORTION, FILTER MEANS IN SAID FILTER CHAMBER INTERMEDIATE SAID INLET AND OUTLET PORTIONS THEREOF FOR INTERCEPTING POWDER PARTICLES FROM A GAS STREAM ADMITTED THROUGH SAID INLET PORTION, COLLECTING MEANS BENEATH SAID FILTER MEANS, VIBRATING MEANS OPERATIVELY CONNECTED WITH SAID FILTER MEANS FOR VIBRAING SAID FILTER MEANS SO AS TO RELEASE INTERCEPTED POWDER PARTICLES FOR COLLECTION OF THE SAME BY SAID COLLECTING MEANS, A SOURCE OF SUCTION, A SUCTION CHANNEL INTERPOSED BETWEEN AND COMMUNICATING WITH SAID SOURCE AND SAID OUTLET PORTION, SAID SUCTION CHANNEL HAVING AN INTAKE PORT FOR AMBIENT AIR AT ATMOSPHERIC PRESSURE FROM THE EXTERIOR OF THE APPARATUS, FIRST VALVE MEANS BETWEEN SAID OUTLET PORTION AND SAID SUCTION CHANNEL TO OPEN AND CLOSE SAID OUTLET PORTION TO SUCTION, SECOND VALVE MEANS IN SAID INTAKE PORT, AND CONTROL MEANS CONNECTED TO SAID VALVE MEANS FOR DISPLACING SAID FIRST AND SECOND VALVE MEANS BETWEEN CLOSED AND OPEN POSITIONS THEREOF SO THAT SAID SOURCE DRAWS SAID GAS STREAM INTO AND THROUGH SAID FILTER CHAMBER AND SAID SUCTION CHANNEL WHEN SAID FIRST VALVE MEANS IS IN SAID OPEN POSITION THEREOF WITH ATTENDANT INTERCEPTION OF THE POWDER PARTICLES FROM SAID GAS STREAM BY SAID FILTER MEANS, WHEREAS AMBIENT AIR FROM THE EXTERIOR OF THE APPARATUS IS DRAWN BY THE SOURCE INTO SAID SUCTION CHANNEL THROUGH SAID
 2. An apparatus as defined in claim 1; and further comprising suspending means for freely swingably suspending said filter elements in said filter chamber.
 3. An apparatus as defined in claim 1, wherein said control means includes means for pneumatically actuating said valve means.
 4. An apparatus as defined in claim 1, wherein said control means is operative for closing said first valve means and opening said second valve means during the operation of said vibrating means whereby the passage of said gas stream through said filter chamber is interrupted and the released powder particles are collected by said collecting means.
 5. An apparatus as defined in claim 1, wherein said filter means comprises substantially upright suspended filter elements having lower end portions; and a vibratory frame engaging said lower end portions; and wherein said vibrating means is connected with said frame for vibrating the same so as to effect release of intercepted powder particles from said filter means for collection in said collecting means, said vibrating means comprising a pneumatic cylinder and piston unit including a piston rod and a weight carried by the latter, and an air-impulse valve cooperating with said unit for imparting oscillatory movement to said weight.
 6. An apParatus as defined in claim 5, wherein said frame is freely swingable, and wherein said vibrating means is located in said chamber and carried by said frame.
 7. An apparatus as defined in claim 6; and further comprising a flexible conduit connecting said vibrating means with a source of hydraulic fluid.
 8. An apparatus as defined in claim 1, wherein said filter means comprises a mounting member, a vibratory frame downwardly spaced from said mounting member, and a plurality of substantially plate-shaped filter elements suspended from said mounting member and including gas-permeable supports having lower end portions engageable by said frame and capable of flexing in the direction in which said frame vibrates, and filter cloths externally surrounding the respective supports so as to flex with the same, whereby powder particles retained on said cloths are released from the same; and wherein said vibrating means is connected with said frame for vibrating the same so as to effect release of said powder particles for collection thereof in said collecting bin.
 9. An apparatus as defined in claim 8, wherein said supports are of wire cloth.
 10. An apparatus as defined in claim 8, wherein said supports each comprise two substantially parallel spaced support sections, and spacer means between said sections so as to maintain them spaced apart.
 11. An apparatus as defined in claim 8, wherein said end portions of said supports have limited freedom of play relative to said frame.
 12. An apparatus as defined in claim 1, and wherein said collecting means comprises a receptacle having a bottom wall subdivided into a plurality of fluidizing sections, and supply means for supplying each of said sections independently with a fluidizing gas so as to fluidize the collected powder particles in said receptacle.
 13. An apparatus as defined in claim 12, wherein said bottom wall is subdivided into two of said fluidizing sections.
 14. An apparatus as defined in claim 12, wherein said bottom wall is substantially horizontal, and wherein said receptacle is of right-angular cross-section and comprises a pair of substantially vertical end walls and a pair of upwardly inclined side walls; and further comprising injector-type conveying means in said receptacle above one of said sections for conveying fluidized powder particles out of said receptacle.
 15. An apparatus as defined in claim 14, wherein said receptacle is of substantially quadratic cross-section.
 16. An apparatus as defined in claim 1; further comprising conduit means for connecting said inlet portion with a spraying station for spraying powder into a workpiece; and wherein said control means includes sensing means for sensing the occurrence of a condition incident to combustion of powder at said station, said control means being operative for closing said first valve means and opening said second valve means in response to a sensing signal received from said sensing means.
 17. An apparatus as defined in claim 16, wherein said sensing means comprises a photoelectric cell.
 18. An apparatus as defined in claim 16, wherein said sensing means comprises a photoelectric cell operative for detecting the occurrence of sparking at said station.
 19. An apparatus as defined in claim 16, wherein said sensing means comprises a sensor capable of sensing the occurrence of at least one of the combustion incident conditions of sparking, deflagration and combustion.
 20. An apparatus as defined in claim 16; further comprising an valve interposed in said conduit means and operative for blocking the same in response to operation of said control means. 